Download Chapter 20. Effects of Processing on the Nutritional Value of Feeds 1

Chapter 20. Effects of Processing on the
Nutritional Value of Feeds
1. INTRODUCTION
2. HEAT TREATMENT
3. GRINDING
4. PELLETING AND CRUMBLING
5. PROCESSING TO DESTROY NATURALLY OCCURRING TOXINS AND
INHIBITORS
6. EFFECT OF PROCESSING ON MOULDS, SALMONELLA, AND OTHER
HARMFUL SUBSTANCES
7. EFFECT OF PROCESSING ON THE AVAILABILITY AND NUTRITIONAL
VALUE OF VITAMINS
8. EFFECT OF PROCESSING ON THE AVAILABILITY AND NUTRITIONAL
VALUE OF TRACE MINERAL ELEMENTS
9. REFERENCES
G. Walker
Western Farmers Association
Seattle, Washington
1. INTRODUCTION
Feeds are processed to facilitate handling and pelleting, and to increase feeding value by
increasing digestibility or by inactivating specific growth inhibitors. Many processes that
facilitate handling and pelleting increase the nutritional value of feeds as well, but the nutritional
value of some feeds can be lowered by certain processes.
2. HEAT TREATMENT
Heat treatment is employed to dry certain plant products and to improve the quality of pelleted
feeds. Heat is sometimes employed in the extraction processes to remove oil from some oilseeds.
Heat treatment improves the nutritional value of soybean meal by destroying the trypsin inhibitor
which is naturally present, and by increasing the utilization of proteins and amino acids, fats, and
carbohydrates present in the meal. Digestibility is enhanced by partial "cooking" and thus the
ME value is increased.
Heat treatment increases the nutritional value of cereal grains by gelatinizing starches and
improving digestibility. This change occurs during steam pelleting, when dry steam is added to
the mixture of feed ingredients just prior to pelleting to condition the feed so that better quality
pellets are produced. Proper conditioning of feeds before pelleting results in improved pellet
durability and a reduced amount of fines in the finished product.
3. GRINDING
Grinding may increase the nutritional value of feeds by reducing the particle size of the
ingredients and thereby increasing the surface area of the ingested feed and facilitating digestion.
In addition, the grinding process adds metals to feeds from the grinding machinery and can
prevent a micromineral deficiency. The metals that are added to feed are Fe, Zn, Cu, Mn, and
Na.
4. PELLETING AND CRUMBLING
The pelleting and crumbling process compacts the mixed feed ingredients and increases nutrient
density and bulk density. For some species, pelleting improves palatability or acceptability of
feeds. As mentioned above, the steam conditioning that occurs just before pelleting may improve
digestibility. The heat generated during compaction of the pellet may also improve digestibility
and destroy thermolabile toxic factors that naturally occur in some plant products. Pelleting
enhances the availability of phosphorus in wheat bran and also permits the use of low density,
bulky, unpalatable feeds that might not otherwise be practical to use.
5. PROCESSING TO DESTROY NATURALLY
OCCURRING TOXINS AND INHIBITORS
5.1 Cottonseed Meal
5.2 Soybean Meal
5.3 Linseed Meal
5.1 Cottonseed Meal
Cottonseed meal contains gossypol, a compound with undesirable nutritional qualities. Free
gossypol is associated with the pigment gland. Puncturing the pigment gland causes free
gossypol to be mixed with other compounds in cottonseed meal and becomes bound. Bound
gossypol is less harmful than is free gossypol.
The method used to remove the cottonseed oil affects the gossypol content of the residue which
becomes cottonseed meal. Hydraulic pressed and solvent-extracted meals contain higher levels
of gossypol than does prepressed solvent meal. Glandless meal has lower levels of gossypol.
Treatment of the meal with iron salts eliminates the toxicity of gossypol, but also produces a
darker meal which is unacceptable to the feed industry (see Table 1).
Treatment of cottonseed meal with phytase increases the availability of phosphorus, reduces
gossypol toxicity, and increases the availability of some proteins.
Table 1. Toxins and Inhibitor Destruction by Processing
Feed Stuff
Cottonseed
Meal
Soybean Meal
Linseed Meal
Raw Fish
Alfalfa Meal
Rye
Sweet Clover
Wheat Germ
Rapeseed
Inhibitor
Gossypol: Cyclopropane fatty acids;
Phytate
Trypsin inhibitor
Crystalline water-soluble substance
Thiaminase
Saponins; pectin methyl esterase
5-N-alkyl resorcinols
Dicoumarol
Unidentified
Isothiocyanate; thyroactive materials
Deactivation Process
Add iron salts; rupture pigment
gland
Heat, autoclaving
Water treatment
Heat
Limit amount fed
Limit amount fed
Heat
5.2 Soybean Meal
Heat destroys the trypsin inhibitor. Wet heat is more effective than dry heat.
5.3 Linseed Meal
The toxic factor for poultry can be removed by soaking the meal in water for 12-18 hours.
6. EFFECT OF PROCESSING ON MOULDS,
SALMONELLA, AND OTHER HARMFUL SUBSTANCES
6.1 Moulds and Mycotoxins
6.2 Salmonella
6.1 Moulds and Mycotoxins
Aflatoxins, produced on some feeds by Aspergillus flavus, are not inactivated by normal
pelleting procedures. Prevention of mould growth is the best means to avoid contamination.
Removal and disposal of mould-damaged material is essential. Certain materials that are
sometimes contaminated by aflatoxins, such as corn, peanut meal, cottonseed meal, copra, and
fish meal, should be monitored routinely to check for the presence of aflatoxins.
6.2 Salmonella
In contrast to aflatoxins, salmonella is killed by pelleting. Meat meal is a feed ingredient that
should be routinely monitored for the presence of salmonella; proper sanitation procedures will
reduce the incidence of contamination.
7. EFFECT OF PROCESSING ON THE AVAILABILITY
AND NUTRITIONAL VALUE OF VITAMINS
Prolonged heat treatment can destroy the fat soluble vitamins and the water soluble vitamins
thiamine, pantothenic acid, folic acid, and biotin. Such heat treatment can occur during the
drying of protein supplements of plant and animal origin. For example, meat and bone meal
contains little or no thiamine as a result of processing. The water soluble B vitamins are removed
to some extent during the processing of fish into fish meal. The B vitamin content of fish-stick water is higher than that of fish meal.
The pelleting process can alter the vitamin content of feeds. If insufficient anti-oxidants are
present in the feed, pelleting may destroy Vitamins A, E, and K. On the other hand, pelleting
may increase the availability of nicotinic acid and biotin, which are often present in feeds in a
bound form.
Certain trace minerals act as pro-oxidants in feeds and can hasten the oxidative destruction of
Vitamins A, D, and E. Manganese and iron are examples of such minerals. Non-nutritive feed
additives, such as bentonite, which are added to feeds as binding agents, may interfere with the
availability of riboflavin and certain divalent cations, such as zinc.
Some commercial methods for processing grains and oilseed meals result in decreased levels of
certain vitamins in the final product. For example, coarse wheat flour grinders lose less Vitamin
E than fine grinders. Germinated wheat may have a Vitamin E level as low as 30 percent of
ungerminated wheat. Solvent extraction of soybean meal results in the removal of some of the
Vitamins E and K and, thus, lower levels in the product.
8. EFFECT OF PROCESSING ON THE AVAILABILITY
AND NUTRITIONAL VALUE OF TRACE MINERAL
ELEMENTS
Generally, the availability of minerals is not affected by processing. The availability of zinc is
sometimes enhanced by addition of the chelate EDTA. Pelleting and crumbling do not affect
trace mineral levels in feed.
9. REFERENCES
National Research Council, 1973 Committee on Animal Nutrition; Center for Tropical
Agriculture, University of Florida; and. Department of Animal Science, University of Florida,
Effect of processing on the nutritional value of feeds. Proceedings of a Symposium, Gainesville,
Florida, January 11-13, 1972. Washington, D.C., National Academy of Sciences, 491 p.